The present invention relates to a method and means for monitoring the performance of mechanical bearings.
Mechanical bearings, such as ball or roller bearings, are designed to operate under predetermined load conditions. When correctly loaded bearings work well. However at loads approaching zero, slippage can occur between components of the bearing. With changing loads the bearing races can move out of their correct optimum positions. Vibration and impact can also damage bearing components. Hitherto it has been difficult to sense the onset of slippage or other conditions giving rise to bearing damage with the result that bearings are generally over-engineered relative to the loading and other conditions under which they are designed to operate.
When a mechanical rolling element bearing operates correctly the surface rotation speed of the rolling elements of the bearing are the same as the differential speed between the inner and outer races. The bearing elements will appear to rotate at around half the differential speed of the inner and outer components of the bearing. If a bearing slips, overheating and damage can result. The surface speed of the rolling elements will reduce and the speed of the cage in which they are mounted will be less than the differential speed of the inner and outer races. Detection of these conditions therefore provides early warning of potential bearing failure.
Hitherto sensing of slippage or other stress conditions in such bearings has been relatively complex. Previous proposals include the use of thermal sensors to detect overheating of the lubricant film in which the bearing operates or have required incorporation of radioactive tracers in the bearing components themselves. Such systems are complex. In addition they operate by detecting slippage and cannot detect overstressing of bearings through other causes. Previous proposals have also included proximity sensors operative to detect the speed of rotation of bearing rolling elements and races.
It is an object of the present invention to provide an improved method and apparatus for monitoring bearing performance.
We have found that bearings subject to stress or slippage generate a significant electrostatic charge, proportional to the degree of stress and a change of charge distribution under slippage. Thus it is possible to sense the condition of a bearing by sensing the resultant change and pattern of electrostatic activity. Accordingly the invention provides a method of anticipating the onset of a deleterious condition in a bearing comprising monitoring the bearing for electrostatic activity indicative of the onset of distress of the bearing or its components.
Preferably the method includes generation of an output signal responsive to detection of said change in electrostatic activity. Said output signal may be employed to actuate indicator or alarm means providing a visual and/or audible warning of the onset of the said condition. Alternatively or in addition said signal may be employed to rectify a condition giving rise to stressing or slippage of the bearing. Thus the output signal may be employed to alter the bearing loading to remove the source of the deleterious condition. Alternatively said output signal may be employed to terminate operation of equipment of which the bearing forms a part to prevent further bearing damage, or to limit the xe2x80x98lifexe2x80x99 or further running of the bearing to prevent failure.
The invention also provides apparatus for anticipating the onset of a deleterious condition in a bearing comprising means for sensing electrostatic activity in the bearing generated in response to the onset of distress of the bearing or its components.
Preferably said means for measuring electrostatic activity comprises an electrostatic sensor adapted to be mounted within sensing proximity range outside the bearing or within the bearing structure and operable to detect changes in electrostatic charge on components of the bearing.
Preferably also the apparatus includes means for generating a signal in response to said changes in activity and means for processing said signal to produce an electrical output.
The apparatus may also optionally include means for detecting individual bearing elements and for processing of signal(s) derived therefrom.
The apparatus may include visual or audible alarm means operable in response to said output to provide a warning of the onset of said deleterious condition. Alternatively or in addition the apparatus may include means operable in response to said output to alter the loading on the bearing to reduce or eliminate said condition. The apparatus may alternatively include means operable in response to said output to interrupt operation of equipment of which said bearing forms a part to prevent further damage to the bearing.
The output signal may be recorded or stored to show events in the bearing life/performance as part of an engine/shaft/bearing health management system. In this way a continuous record of bearing performance over time may be produced and may be employed to predict remaining or used bearing life.